1. Field of the Invention
The present invention relates to an optical sensor device in which an optical sensor element is mounted on a package material using a glass substrate.
2. Description of the Related Art
In recent years, mobile terminals such as mobile personal computers, tablet personal computers, and smartphones are rapidly becoming widespread. Further, flat screen televisions and LED lighting for inside and outside lighting devices are significantly becoming widespread. The reason behind this is because those mobile terminals have a large number of functions and another main reason is that they are designed to promote portability such as light in weight and thin in thickness. At the same time, in the fiat screen televisions, and the inside end outside lighting devices, there has been a development problem of an energy-saving rate along with an increase in performance year after year, and many of the televisions and devices have a function of controlling the illuminance finely. The number of electronic parts used in those mobile terminals, fiat screen televisions, and the inside and outside lighting devices is numerous along with the pursuit of multi-functionality and portability, and further reduction in size, thickness, and cost and power saving in electronic parts are now always required. As a result, a resin mold package has been widely adopted. The reason behind this is the common use of parts and materials. An optical sensor, which is a one of electronic parts mounted to reduce the power consumption, is not exceptional. Similar to other electronic parts, reduction of the size, thickness, and cost are aimed at in marry optical sensor products by the use of resin mold package.
FIG. 2 of Japanese Published Patent Application No. 2007-36264 discloses a cross-sectional view of an illuminance sensor package in which a light receiving element is mounted on an insulating substrate made of a resin material and is molded by a resin. An electrode 4 is formed on the front surface of a resin substrate 1. The electrode 4 is wired so as to surround the rear surface of the substrate from the front surface of the substrate, thereby being connectable to the outside. The electrode 4 has an optical sensor element 1 mounted thereon. A top surface 2a of the optical sensor element 2 and the electrode 4 are electrically connected via a wire 6. The optical sensor element 2 is firmly fixed onto the electrode 4 by a conductive paste 5. The conductive paste 5 electrically connects the optical sensor element 2 and the electrode 4 to each other. Electromotive force generated by light entering the optical sensor element 2 can flow from the conductive paste 5 to the electrode 4 so as to be transmitted to the outside.
In Japanese Published Patent Application No. 2007-36264, the optical sensor element 2 is molded by a resin 11 as a whole. The resin 11 is made of a translucent resin, and an epoxy resin or the like is used. An infrared absorbing film 12 is provided on the resin 11. The infrared absorbing film 12 uses a resin and has a structure in which a liquid resin or a film is adhered and laminated on she resin 11. As the liquid resin, an epoxy resin or the like is used. In the case of using a film, a film is adhered on the resin 11 via a resin adhesive. With this, the optical sensor element 2 can receive visible light from which infrared light has been filtered, thereby serving as an optical sensor corresponding to the visibility. Such infrared absorbing effect can also be obtained even when an infrared absorbing substance used for the infrared absorbing film 12 is dispersed and mixed in the translucent resin 11.
However, the optical sensor device described in Japanese Published Patent Application No. 2007-36264 has a package structure in which an epoxy resin or the like is used for sealing the element, and hence has a problem such as weak in environmental reliability including heat resistance and moisture resistance of the material. Further, the resin used for sealing the element is required to be translucent, and thus, it is generally thought to be difficult for the resin to be resistant to heat at the same time. Further, the sealing resin seals the optical sensor element 2 and the wire 6, and thus, design for alleviating stress on the optical sensor element and the wire is necessary, requiring low stress. It follows that the range of selection of the sealing resin which significantly determines the reliability of the device is limited: low resistance to heat; low stress; easy to take up moisture; easy to expand at a high temperature; and the like. As a result, it is difficult to obtain high performance in an environment in which heat and moisture are added or in an environment in which expansion and contraction are repeated in a temperature cycle repeating high temperature and low temperature as in a reliability test.
Further, in the optical sensor device described in Japanese Published Patent Application No. 2007-36264, a resin such as an epoxy resin is used as an example for sealing the optical sensor element 2. In this case, the resin may be decomposed by moisture, heat, ultraviolet radiation, or the like. It is known that, as a result, the sealing resin is gradually deteriorated and exhibits discoloration or the like, and at the same time, the transmittance thereof is lowered. As a result, there is a problem that light is less liable to enter the optical sensor element, and desired properties and reliability as art optical sensor device cannot be obtained.
Further, in the optical sensor device described in Japanese Published Patent Application No. 2007-36264, the optical sensor element 2 and the electrode 4 electrically connected to the upper surface 2a of the optical sensor element 2 via the wire 6 are mounted on the same surface, and the electrode 4 is used for connection to the outside. In the case of this structure, in order to reduce the size of the optical sensor device, the distance between the external electrode 4 electrically connected to the mounted substrate and the optical sensor element 2 and the length of the wire 6 are required to be short, and thus, it is required that, for example, the thickness of the resin which seals the optical sensor element 2 be small. As a result, for example, in reflowing carried out in a process of mounting the optical sensor device, phenomena such as wicking and erosion of solder paste used for connection to the mounted substrate are accompanied by entry of the solder paste from between the sealing resin and the electrode 4, and a risk of separation of the wire or separation from the sealing resin increases.
FIG. 1 of Japanese Published Patent Application No. 2007-234783 discloses a cross-sectional view of a light receiving sensor package in which a light receiving element is mounted on a leadframe and sealed by a resin mold. In the optical sensor device described in Japanese Published Patent Application No. 2007-234783, with regard to change in the properties and lowered reliability of the above-mentioned optical sensor device described in Japanese Published Patent Application No. 2007-36264, by containing an inorganic filler in a sealing resin material, the coefficient of thermal excursion is adjusted, and the resin is improved to have a certain effect. This improvement obtains the effect of improving performance in an environment in which expansion and contraction are repeated in a temperature cycle repeating high temperature and low temperature, which causes a problem of a conventional sealing resin material. A certain effect is expected also with regard to improvement in the heat resistance.
Further, in the optical sensor device disclosed in Japanese Published Patent Application No. 2007-234783, the distance between an optical sensor element 10 and a lead portion 22 for external connection of a leadframe 20 electrically connected to an upper surface of the optical sensor element 10 via a wire 25 is relatively large. As a result, separation between the leadframe 20 and the wire 25 and separation between a sealing resin 30 and the leadframe 20 caused by wicking or erosion of solder paste in mounting such as relieving can be inhibited.
The optical sensor device described in Japanese Published Patent Application No. 2007-234783 obtains the effect by containing an inorganic filler in a transparent epoxy resin or the like for sealing, but, when an inorganic filler is mixed in a resin, it is known that air exists at an interface between the inorganic filler and the resin a rut that it is not easy to mix the inorganic filler in the resin so that the refractive index and the surface state of the inorganic filler do not lower the optical properties of the transparent sealing resin at all. As the content of the inorganic filler increases, the reliability improves more, but the transmittance lowers, and thus, light is less liable to enter the optical sensor element 10, and the device does not function as an optical sensor device. Accordingly there is a possibility that the effect of improving the reliability of the optical sensor device by adding inorganic filler is limited.
Further, the optical sensor device described in Japanese Published Patent Application No. 2007-234783 has the lead portion 22 for external connection of the leadframe 20, the lead portion 22 being relatively away from the optical sensor element 10 and protruding significantly from the sealing resin 30, and thus, the reliability in mounting is improved, but the package size is liable to increase, and it is difficult to enjoy the merits of miniaturization. Accordingly, it is difficult to accommodate the use where portability is required.
Under these circumstances, an electronic part in which glass is used for a package material is partly in actual use. A glass material prevents moisture and contaminants from entering from the outside, and maintains high airtightness. Further, since the glass material has a thermal expansion coefficient which is close to that of a silicon substrate forming a semiconductor element, reliability of the mounting surface and the bonding surface can be enhanced when the semiconductor element is mounted on a glass package. Further, since the glass material is inexpensive, increase in product cost can be suppressed.